Back to EveryPatent.com
United States Patent |
5,719,979
|
Furuyama
|
February 17, 1998
|
Optical semiconductor module and method for manufacturing the same
Abstract
An optical semiconductor module comprises an optical semiconductor element,
an optical fiber, a monocrystalline substrate, an airtight sealing member
and a reinforcing plate. Light is transmitted through the optical
semiconductor element and the optical fiber. The optical semiconductor
element and the optical fiber are mounted on the monocrystalline
substrate. The optical semiconductor element is sealed airtight by the
airtight sealing member. An optical axis aligning mechanism for aligning
the optical axis of the optical semiconductor element with the optical
axis of the optical fiber is arranged on the monocrystalline substrate.
The reinforcing body is welded with metal on the rear surface of the
monocrystalline substrate.
Inventors:
|
Furuyama; Hideto (Yokohama, JP)
|
Assignee:
|
Kabushiki Kaisha Toshiba (Kawasaki, JP)
|
Appl. No.:
|
531640 |
Filed:
|
September 21, 1995 |
Foreign Application Priority Data
Current U.S. Class: |
385/89; 385/91; 385/94; 438/25; 438/978 |
Intern'l Class: |
G02B 006/43 |
Field of Search: |
385/88-94,65,59
156/650.1,654.1,657.1
|
References Cited
U.S. Patent Documents
4897711 | Jan., 1990 | Blonder et al. | 385/88.
|
5307434 | Apr., 1994 | Blonder et al. | 385/91.
|
5412748 | May., 1995 | Furuyama et al. | 385/92.
|
5444805 | Aug., 1995 | Mayer | 385/49.
|
5535296 | Jul., 1996 | Uchida | 385/89.
|
5555333 | Sep., 1996 | Kato | 385/89.
|
Foreign Patent Documents |
1219806 | Sep., 1989 | JP | 385/65.
|
6-67036 | Mar., 1994 | JP | 385/88.
|
Other References
K.P. Jackson et al., "A Compact Multichannel Transceiver Using
Planar-Processed Optical Waveguides and Flip-Chip Optoelectronic
Components", Proceedings of the 42nd Electronic Components & Technology
Conference, p. 94 (1992). ›No month!.
|
Primary Examiner: Lee; John D.
Assistant Examiner: Kang; Ellen E.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow, Garrett & Dunner, L.L.P.
Claims
What is claimed is:
1. An optical semiconductor module adapted to a plurality of optical
transmission and reception channels, comprising:
a monocrystalline substrate having first and second surfaces;
an optical semiconductor array formed on the first surface of the
monocrystalline substrate, having a plurality of optical axes, for
performing light emitting and receiving functions;
an optical fiber array formed on the first surface of the monocrystalline
substrate, having a plurality of optical axes, for transmitting light
received and emitted by the optical semiconductor array;
an optical axis aligning mechanism, formed on the first surface of the
monocrystalline substrate, for aligning the optical axes of the optical
semiconductor array with the optical axes of the optical fiber array;
an airtight sealing member formed on the first surface of the
monocrystalline substrate for forming an airtight seal around the optical
semiconductor array and a portion of the optical fiber array; and
a reinforcing body formed on the second surface of the monocrystalline
substrate and thermally connected to a part of the airtight sealing
member, and having a thermal expansion characteristic substantially equal
to that of the airtight sealing member.
2. The optical semiconductor module according to claim 1, wherein the
reinforcing body is soldered by metal to the second surface of the
monocrystalline substrate.
3. The optical semiconductor module according to claim 1, wherein a
material and a shape of a mount surface of the reinforcing body are
determined depending on characteristics of the monocrystalline substrate.
4. The optical semiconductor module according to claim 1, wherein a
material of the reinforcing body is determined depending on a material of
the airtight sealing member.
5. The optical semiconductor module according to claim 1, wherein the
reinforcing body has a shape which defines an arrangement on the
monocrystalline substrate.
6. The optical semiconductor module according to claim 1, wherein the
reinforcing body and the airtight sealing member are formed of materials
selected from the group consisting of metal, ceramics and thermoplastic.
7. The optical semiconductor module according to claim 1, wherein the
monocrystalline substrate has an Si substrate.
8. The optical semiconductor module according to claim 1, wherein the
monocrystalline substrate includes:
an engaging groove for aligning the optical axes of the optical fiber array
with the optical axes of the optical semiconductor array, such that the
monocrystalline substrate does not contact the optical fiber array.
9. The optical semiconductor module according to claim 1, wherein a part of
a peripheral portion of the airtight sealing member is connected to the
reinforcing body, and the monocrystalline substrate is arranged inside a
connect portion of the airtight sealing member.
10. The optical semiconductor module according to claim 1, further
comprising:
an optical fiber array holder for holding a portion of the optical fiber
array which projects from the first surface of the monocrystalline
substrate.
11. The optical semiconductor module according to claim 10, wherein:
the optical fiber array holder is formed on the first surface of the
monocrystalline substrate and aligns the optical axes of the optical
semiconductor array with the optical axes of the optical fiber array.
12. The optical semiconductor module according to claim 10, wherein:
the optical fiber array holder is comprised of a plurality of optical fiber
holder members.
13. The optical semiconductor module according to claim 10, wherein:
The optical fiber array holder defines a position on the first surface of
the monocrystalline substrate at which the optical fiber array holder is
mounted, and
the optical axes of the optical semiconductor array and the optical axes of
the optical fiber array are aligned with each other by mounting the
optical fiber array holder to the defined position on the first
monocrystalline substrate surface.
14. The optical semiconductor module according to claim 10, wherein the
monocrystalline substrate includes:
an engaging groove for aligning the optical axes of the optical fiber array
with the optical axes of the optical semiconductor array, such that the
monocrystalline substrate is not brought into contact with the optical
fiber array holder.
15. A method for producing an optical semiconductor module, wherein a
composite pattern of a combination of grooves having different widths is
formed on a plane of an Si substrate by anisotropic etching in which
etching is substantially stopped at the plane, and thereafter an optical
fiber is fixed to the composite pattern, the method comprising the steps
of:
forming a wider groove by etching on the Si substrate, using a first
rectangular window mask; and
forming a narrower groove by etching on the Si substrate, using a synthetic
mask comprising a second rectangular window, a predetermined distance
apart from the wider groove, and a band-shaped window which is narrower
than the second rectangular window and extending from a slant face on a
contact portion of the wider groove to the second rectangular window.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical semiconductor module wherein
optical coupling of an optical semiconductor element and an optical
waveguide need not be adjusted.
2. Description of the Related Art
In the field of optical fiber communication, an optical semiconductor
module is used, in which optical semiconductor elements, i.e., a laser
diodes (a light emitting element) or a light detection element, etc.,
serving as a signal transmission path are optically coupled, and the
optically coupled semiconductor elements and the optical fiber are
packaged in an airtight sealing (hermetic sealing) package.
This type of optical semiconductor module is much more expensive than a
semiconductor module in which electronic semiconductor elements, such as
transistors and ICs, are packaged. This is not because the manufacturing
an optical semiconductor element requires a high cost, but mainly because
the cost of adjusting optical coupling of an optical semiconductor element
and an optical waveguide, such as an optical fiber, is high due to the
difficulty in improving the throughput.
In general, an optical semiconductor element and an optical fiber must be
positioned with accuracy in the micron order. Positioning by mechanical
means, such as a guide mechanism or the like, has a drawback that a mount
base, on which the semiconductor elements are mounted, must be worked with
great accuracy and complicated, and therefore the base manufacturing cost
is considerably increased.
To overcome this drawback, in a conventional optical semiconductor module,
an optical semiconductor element and an optical fiber are individually
mounted on independent bases or holders. The semiconductor element and the
optical fiber mounted on the independent bases or holders are separately
examined, and the bases or holders are faced each other, thereby achieving
optical coupling. For this reason, mechanical positions of the optical
semiconductor element and the optical fiber must be adjusted. In this
case, so-called optical coupling adjustment is required, wherein mounting
positions are adjusted, while the intensity of an optical input or output
is being monitored.
The optical semiconductor element, as described above, must be sealed
airtight by a package to ensure reliability, so that a light input/output
surface of the optical semiconductor element can be protected. The
airtight sealing is achieved by sealing an airtight sealing member made of
metal, glass, ceramics or the like, with fusion bonding of metal or glass.
For this reason, the sealing step requires a considerably high temperature
and the airtight sealing member is thermally deformed greatly.
In a conventional optical semiconductor module, an optical semiconductor
element is optically coupled with an optical fiber, after the
semiconductor element is sealed airtight. If optical coupling is performed
before the sealing step, the mechanical positions may be shifted, since
the airtight sealing member easily deformed by heat in the sealing step.
In this case, since the optical semiconductor element, which has been
sealed, must be optically adjusted to the optical fiber, it is difficult
to mechanically detect the mounting position of the optical semiconductor
element due to the airtight sealing member. In other words, since
positioning cannot be achieved by a guide mechanism, it is difficult to
reduce a time required for the step by coarse adjustment of the positions
of the optical axes of the optical semiconductor element and the optical
fiber by mechanical means. Therefore, the optical axis adjustment, which
generally requires accuracy of the micron order, must be performed
entirely by optical position detecting means.
Further, after the adjustment of the optical axis, it is necessary to
mechanically fix the semiconductor element and the optical fiber firmly to
prevent a shift of the optical axis. However, the optical axis may be
shifted during the mechanical fixation, since the positional relationship
between the members to be fixed is changed, depending on the adjusted
state of the optical axis, and the state varies even in the same process
conditions.
As described above, in the conventional optical semiconductor module, the
throughput cannot easily be improved due to the difficulty in reducing the
time required for the step of adjusting optical coupling. In addition, the
manufacturing yield cannot be easily improved, because the positional
relationship between the members to be fixed is different in every module.
Accordingly, the cost for adjusting optical coupling is increased,
resulting in a considerably high module cost.
Under the circumstances, there is a demand for an optical semiconductor
module, whose manufacturing yield can be improved easily and which can be
mass-produced. Some trials for such an optical semiconductor module have
been proposed. Of the trials, an optical semiconductor module by
application of so-called micromachining, one of the semiconductor
manufacturing techniques, has attracted public attention. Since the module
produced by the application of the micromachining can be machine-processed
with a higher degree of accuracy, i.e., in the submicron order, the
positions of an optical semiconductor element and an optical fiber can be
adjusted with the accuracy of the micron order by mechanical assembling
only, which overcomes a basic problem of the conventional semiconductor
module. In other words, optical coupling of an optical semiconductor
element and an optical fiber can be achieved only by a mechanical
assembling step and adjustment of optical axes as described above is not
required. Moreover, since a number of bases can be mass-processed in the
same manner as in the case of manufacturing optical semiconductor
elements, the cost for processing mount bases is considerably reduced as
compared to the conventional cutting processing by means of a machine.
With the above technique, the cost of producing optical semiconductor
modules can be reduced and the production yield can be considerably
improved. Further, signal transmission of a large capacity and a high
quality, which is characteristic to the optical communication technique,
can be introduced to industrial machines such as an optical
interconnection. As a result, a high speed and high performance system can
be constructed, which greatly contributes to development and progress of
industry.
However, in the optical semiconductor module to which the micromachining
technique is applied, since only the improvement of optical coupling is
taken into account, another requirement for practicality, i.e., airtight
sealing, has not been achieved. For this reason, such an optical
semiconductor module is far from practical use. Drawbacks of the
conventional art will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view of an example of the conventional optical
semiconductor module, to which the micromachining is applied. As shown in
FIG. 1, the optical semiconductor module comprises an Si substrate 1, an
optical fiber 5, an optical semiconductor element 6, an IC 7 for driving
the optical semiconductor element 6, and a bonding wire 17. The module
further comprises an airtight sealing cap 28, a position adjusting groove
2, an airtight sealing solder 10 for connecting the airtight sealing cap
28 with the Si substrate 1, the airtight sealing solder 16, a solder 18
for the optical semiconductor element 6 on the Si substrate 1, an
electrical wiring conductor 26 and an insulator 27.
In this example, the optical fiber 5 is fixed to the position adjusting
groove 2 of the Si substrate 1, so that the positional relationship to the
optical semiconductor element 6 can be mechanically self-alignment.
Therefore, optical coupling can be achieved through mechanical assembling
steps of mounting the optical semiconductor element 6 to the Si substrate
1 and inserting the optical fiber 5 to the position adjusting groove 2.
The reason why the mounting base is formed of the Si substrate 1 is that
the position adjusting groove 2 can be machine-processed by the
aforementioned micromachining.
Since, in general, an Si monocrystalline (single-crystalline) substrate can
be anisotropically etched due to crystal orientation, it can be processed
into various geometric shapes. A typical shape of a groove for the optical
semiconductor module is a so-called V groove having slants of (111) planes
on both sides, obtained in a case where a slit-like mask in <110> or
<-110> direction is formed on the (100) crystalline plane. Monocrystalline
Si has a characteristic that the (111) plane is etched much more slowly
than the crystalline planes (100) and (110), when etched by an aqueous
solution of KOH or hydrazine. The reference numerals (100), (110), and
(111) denote the crystalline plane. The reference numerals <110> and
<-110> denote the crystal axis.
In the aforementioned anisotropic etching, a V groove can be easily formed
utilizing the crystal orientation and the mask used in the etching can be
formed in the conventional semiconductor process. Thermal oxidation
SiO.sub.2 obtained by heat-treating an Si substrate in an oxide atmosphere
or an Si.sub.3 N.sub.4 by CVD (Chemical Vapor Deposition) method is used
as a mask in the etching. It is fully possible that the machine processing
accuracy obtained by the system is as low as 1 .mu.m, depending on etching
conditions and setting of the mask.
As described above, the optical semiconductor module, to which the
micromachining is applied, is effective to omit adjustment of the optical
coupling. However, since the main purpose of such a module is to omit
adjustment of the optical coupling, an airtight sealing mechanism of the
optical semiconductor element is not necessarily taken into consideration.
Although there has not been many proposals to solve the problems of the
airtight sealing mechanism, an example of the solutions is suggested in
PROCEEDING of 42nd ELECTRONIC COMPONENTS & TECHNOLOGY CONFERENCE (1992),
page 94, FIG. 1. In this example, an airtight sealing cap, for sealing an
optical semiconductor element mounting region, is mounted on an Si
substrate formed by the micromachining process, thereby achieving partial
airtight sealing on the Si substrate. This example is applied to the
aforementioned optical semiconductor module utilizing the micromachining,
so that the structure shown in FIG. 1 can be easily obtained.
With the above structure, the optical semiconductor element and the optical
fiber can be optically coupled with each other by mechanical assembling,
and airtight sealing of the optical semiconductor element can be achieved.
As a result, the cost of producing optical semiconductor modules can be
reduced and the production yield can be considerably improved, so that the
above-described effects can be obtained.
However, the optical semiconductor module thus obtained, still having
drawbacks from the viewpoint of the practical use, cannot be used in
practice. More specifically, in the structure of FIG. 1, an Si substrate
is used as a mount base to make the best use of advantages of the
semiconductor process technique. However, if the airtight sealing cap 28
is formed of a metal selected to secure airtightness, the thermal
expansion characteristic of the Si substrate is not necessarily conform to
those of the other members. Further, when a number of electric wiring
conductors 26 are required, for example, when optical fibers are arrayed
and several tens of leader lines of wiring conductors 26 are required,
thermal deformation stress applied to the Si substrate is not negligible,
since the area of the Si substrate is increased due to the increase of the
number of wiring leaders and the accumulated amount of thermal deformation
of the wiring leaders. The thermal deformation results in problems, such
as a crack of the Si substrate or package leak due to degradation of the
mechanical strength of the airtight sealing portion. Such a problem is
liable to lower the reliability of the optical semiconductor module. As a
result, the yield in consideration of the reliability is lowered and the
advantage obtained by simplification and reduction of the optical coupling
steps is lost.
The above problem of low reliability mainly results from the mechanical
fragility of Si, the material of the substrate. If, therefore, the
substrate is made of ceramics like the general semiconductor package, the
problem of low reliability is diminished. However, if the substrate is
made of ceramics, various problems arise and the essential object of
improving the module is missed. For example, since crystal anisotropy
cannot be utilized in the etching process, the accuracy of the etching
process is as low as several tens of microns. In addition, the cost of the
material of the substrate is increased, or the thermal conductivity of the
substrate is lowered. Therefore, it is necessary to give priority to the
mechanical workability which is required to omit the adjustment of the
optical axis in the optical semiconductor modules. For this reason, use of
an Si substrate is indispensable.
As described above, the conventional optical semiconductor module has a
limit in reduction of the cost due to the adjustment of the optical axis,
whereas application of the micromachining technique, as means for reducing
the cost, lacks practicality.
In the conventional semiconductor package, thermal deformation stress
applied to the Si substrate is not negligible, since the area of the Si
substrate is increased due to the increase of the number of wiring leaders
and the accumulated amount of thermal deformation of the wiring leaders.
The thermal deformation results in problems, such as a crack of the Si
substrate or package leak due to degradation of the mechanical strength of
the airtight sealing portion. Such a problem is liable to lower the
reliability of the optical semiconductor module. As a result, the yield in
consideration of the reliability is lowered and the advantage obtained by
simplification and reduction of the optical coupling steps is lost.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above problems
of the conventional art. Accordingly, a first object of the present
invention is to provide an optical semiconductor module, in which a crack
of the monocrystalline substrate due to thermal deformation stress on
account of the airtight sealing member, so that the productivity and
reliability can be improved.
A second object of the present invention is to provide a method for
producing an optical semiconductor module for easily producing a reliable
optical semiconductor module.
The above objects can be achieved by an optical semiconductor module
comprising:
an optical semiconductor element having an optical axis and performing at
least one of light emitting and receiving functions;
an optical waveguide body, having an optical axis, for transmitting light
in association with the optical semiconductor element;
a monocrystalline substrate, having first and second surfaces, the optical
semiconductor element and the optical waveguide body being mounted on the
first surface;
an airtight sealing member, formed on the first surface of the
monocrystalline substrate, encircling the optical semiconductor element;
and
a reinforcing body arranged on the second surface of the monocrystalline
substrate.
The above objects can be also achieved by an optical semiconductor module
comprising:
an optical semiconductor element having an optical axis and performing at
least one of light emitting and receiving functions;
an optical waveguide body, having an optical axis, for transmitting light
in association with the optical semiconductor element;
an Si substrate, having first and second surfaces, the semiconductor
element and the optical waveguide body being mounted on the first
substrate, and an optical axis aligning mechanism for aligning the optical
axis of the optical semiconductor element with the optical axis of the
optical waveguide body being formed on the first surface;
an airtight sealing member, having a main portion and a peripheral portion,
the main portion being located on the first surface of the Si substrate;
and
a reinforcing body, having a thermal expansion characteristic substantially
the same as that of the airtight sealing member, arranged on the second
surface of the monocrystalline substrate and connected to the peripheral
portion of the airtight sealing member.
Further, the above objects can be achieved by an optical semiconductor
module comprising:
an optical semiconductor element having an optical axis and performing at
least one of light emitting and receiving functions;
an optical waveguide body, having an optical axis, for transmitting light
in association with the optical semiconductor element;
an Si substrate, having first and second surfaces, the semiconductor
element and the optical waveguide body being mounted on the first
substrate, and an optical axis aligning mechanism for aligning the optical
axis of the optical semiconductor element with the optical axis of the
optical waveguide body being formed on the first surface;
an optical fiber holder, arranged on the first surface of the Si substrate,
for holding the optical fiber; and
an airtight sealing member, formed on the first surface of the Si
substrate, encircling and sealing the optical semiconductor element and
the optical fiber holder.
Furthermore, the above objects can be achieved by an optical semiconductor
module comprising:
a guide pin for adjusting a position of an optical connector;
an Si substrate having an adjustment groove for adjusting a position where
the guide pin is to be connected;
a reinforcing body on which the Si substrate is mounted; and
a fixture member, to which the guide pin is fixed, having a spring
mechanism for pressing the guide pin into the adjustment groove of the Si
substrate.
The above objects can also be achieved by a method for producing an optical
semiconductor module comprising:
a guide pin for adjusting a position of an optical connector;
an Si substrate having an adjustment groove for adjusting a position where
the guide pin is to be connected;
a reinforcing body on which the Si substrate is mounted; and
a fixture member, to which the guide pin is fixed, having a spring
mechanism for pressing the guide pin into the adjustment groove of the Si
substrate, the method comprising the steps of:
assembling the fixture member and the guide pin;
fixing the fixture member to the reinforcing plate; and
fixing the fixture member to the guide pin by non-contact welding.
Further, the above objects can be achieved by a method for producing an
optical semiconductor module, wherein a composite pattern of a combination
of grooves having different widths is formed on a plane of an Si substrate
by anisotropic etching in which etching is substantially stopped at the
plane, and thereafter an optical fiber is fixed to the composite pattern,
the method comprising the steps of:
forming a wider groove by etching on the Si substrate, using a first
rectangular window mask; and
forming a narrower groove by etching on the Si substrate, using a synthetic
mask comprising a second rectangular window, a predetermined distance
apart from the wider groove, and a band-shaped window which is narrower
than the second rectangular window and extending from a slant face on a
contact portion of the wider groove to the second rectangular window.
According to the optical semiconductor module of the present invention,
since the optical semiconductor element can be optically coupled with the
optical waveguide body, such as an optical fiber, only by mechanical
assembling, the cost for optical axis adjustment is not required and the
reliability of the airtight sealing structure is ensured. In addition,
since a high reliability is obtained even when the module structure can be
formed as an optical connector connection type, reliable optical
semiconductor module can be produced with a high productivity. Therefore,
the present invention is advantageous in that the manufacturing cost is
considerably reduced and the application range is widened. Further, if
force in a direction so as to bend the monocrystalline substrate is
applied to the substrate due to the stress of the airtight sealing member,
the bent can be reduced or set off by the reinforcing body or reinforcing
member formed on the rear surface of the monocrystalline substrate.
Therefore, the monocrystalline substrate is not cracked.
Additional objects and advantages of the invention will be set forth in the
description which follows, and in part will be obvious from the
description, or may be learned by practice of the invention. The objects
and advantages of the invention may be realized and obtained by means of
the instrumentalities and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part
of the specification, illustrate presently preferred embodiments of the
invention and, together with the general description given above and the
detailed description of the preferred embodiments given below, serve to
explain the principles of the invention.
FIG. 1 is a cross-sectional view of a conventional optical semiconductor
module;
FIG. 2 is a cross-sectional view of an optical semiconductor module
according to a first embodiment of the present invention;
FIGS. 3 to 5 are perspective views of reinforcing members;
FIG. 6 is a schematic diagram showing an Si substrate used in the module
according to the first embodiment;
FIGS. 7A and 7B are diagrams showing a first example of anisotropic etching
of Si according to the first embodiment;
FIGS. 8A and 8B are diagrams showing a second example of anisotropic
etching of Si according to the first embodiment;
FIGS. 9A and 9B are diagrams showing a third example of anisotropic etching
of Si according to the first embodiment;
FIG. 10 is a cross-sectional view taken along the line X--X in FIG. 6;
FIG. 11 is a cross-sectional view taken along the line XI--XI in FIG. 6;
FIG. 12 is an exploded view of parts of the optical semiconductor module of
the first embodiment;
FIG. 13 is a schematic diagram showing an Si substrate used in an optical
semiconductor module according to a second embodiment of the present
invention;
FIGS. 14 and 15 are schematic diagrams showing an Si substrate used in an
optical semiconductor module according to a third embodiment of the
present invention;
FIG. 16 is a cross-sectional view showing an example of a guide pin fixing
portion of the optical semiconductor module of the third embodiment;
FIG. 17 is a cross-sectional view showing another example of a guide pin
fixing portion of the optical semiconductor module of the third
embodiment;
FIG. 18 is a cross-sectional view of an optical semiconductor according to
a fourth embodiment of the present invention; and
FIG. 19 is a cross-sectional view of an optical semiconductor according to
a fifth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will be described with reference to
the accompanying drawings.
(First Embodiment)
An optical semiconductor module according to a first embodiment of the
present invention comprises an Si substrate 1, i.e., a mount base, as
shown in FIG. 2. An optical semiconductor element 6 and an IC 7 for
transmitting or receiving data to or from the optical semiconductor
element are mounted on one surface of the Si substrate 1 via solder. An
optical axis alignment mechanism is formed on the surface of the Si
substrate 1 by the known semiconductor processing technique. The optical
axis alignment mechanism includes a guide groove 2 of an optical fiber 5,
a portion for defining the mounting position of the optical semiconductor
element 6, a metallize and the like. The Si substrate 1 has a solder
groove 3, which is filled with airtight sealing solder 10 surrounding an
optical fiber 5.
The optical semiconductor module of this embodiment comprises a reinforcing
plate 8 for preventing the Si substrate 1 from thermal deformation. As
shown in FIG. 3, the reinforcing plate 8 is a box having a bottom surface
8a for receiving the Si substrate 1 and walls on the three sides of the
bottom. One end of the reinforcing plate 8 does not have a wall so that
optical fibers 5 can be drawn out. The reinforcing plate 8 is need not be
plate-shaped, but can be prismatic reinforcing members. A structure as
shown in FIG. 4 or 5 can be used as the reinforcing plate 8.
The optical semiconductor module of this embodiment comprises an airtight
sealing member. The airtight sealing member is arranged over the Si
substrate 1 and the reinforcing plate 8. The airtight sealing member
comprises a lower frame 11, an airtight sealing insulator 12, an
electrical signal pin 13, an airtight sealing insulator 14, an upper frame
15 and an airtight sealing cap 16.
In the optical semiconductor module of this embodiment, the electrical
signal pin 13 is extended from first end portions of the Si substrate 1
and the reinforcing plate 8. The electrical signal pin 13 is connected to
the IC 7 through a bonding wire 17. The optical semiconductor element 6 is
connected to the IC 7 also through a bonding wire 17. The optical
semiconductor element 6 is optically coupled with the optical fiber 5.
In this embodiment, the Si substrate, having a mechanism for mechanically
adjusting an optical axis, is mounted on the reinforcing plate 8 and the
airtight sealing member is provided thereon. With this structure, the
optical semiconductor element 6 is sealed airtight by sealing the bottom
of the airtight sealing member with the Si substrate 1. Thermal
deformation of the Si substrate 1 and the upper frame 15 of the airtight
sealing member is minimized by using suitable material and structure of
the reinforcing member 8.
A table indicated below shows the combination of the materials of the
reinforcing plate and the sealing member (the sealing cap, the upper
frame, the lead frame, the airtight sealing insulator and the lower
frame). The following case A is employed as the reinforcing plate and the
sealing member of this embodiment.
TABLE
______________________________________
Member Case A Case B Case C
______________________________________
Reinforcing metal ceramics metal
plate (Kovar) (Kovar)
Sealing cap metal ceramics thermoplastic
(Kovar) or metal or metal
(Kovar) (Kovar)
Upper frame metal Non metal (Kovar)
(Kovar) or Non
Airtight glass ceramics thermoplastic
sealing
insulator
Lead frame metal metal metal (Kovar)
(Kovar) (Kovar)
Airtight glass ceramics thermoplastic
sealing
insulator
Lower frame metal Non metal or Non
(Kovar) (Kovar)
______________________________________
General requirements for the materials of the reinforcing plate and the
sealing member of the present invention and notes on the above table will
be described below.
(1) Either metal or ceramics can be used as the reinforcing plate. The
combination of the reinforcing plate of ceramics and the upper frame of
metal or the combination of the reinforcing plate of metal and the upper
frame of ceramics can be used.
(2) The lead frame is formed of a metal is an electric conductor. Kovar
(Ni: 29%, Co: 17%, Fe: balance) is most generally used as the adhesive
sealing compound. However, an Ni--Fe alloy (Ni: 42%, Fe: balance) or a
copper alloy containing a small amount of Cr and Zr can also be used.
(3) Alumina (Al.sub.2 O.sub.3) or aluminum nitride (AlN) can be used as
ceramics.
(4) EVOH, PVdC, PCTFE, or LCP can be used as thermoplastics.
(5) When ceramics are used, a portion of the ceramics to be connected with
metal is metallized and thereafter brazed with the metal or soldered.
(6) When thermoplastic is used, it is only necessary that the plastic be
molded so as to cover the substrate and a special bonding process is not
required.
(7) The above combination of the reinforcing plate and the sealing member
should be determined such that the thermal expansion characteristic of the
Si substrate 1 and those of the reinforcing plate and the sealing member
are well balanced.
Thermal deformation of the Si substrate 1 and the airtight sealing member
(11 to 16) generally occurs in a step of assembling an optical
semiconductor module or a reflow soldering step in process of mounting the
module on a circuit board. However, it can occur even after the module is
mounted on the circuit board, due to an internal temperature distribution
on the apparatus in which the circuit board is mounted, or a change in the
ambient temperature.
The most simple method for suppressing the thermal deformation due to the
distribution or change of the temperature is as follows: using the same
material to form the parts (11 to 16) of the airtight sealing member,
particularly, the frames 11 and 15 and the airtight sealing cap 16 (which
are generally formed of metal), using the reinforcing plate 8 made of the
same material and of the same shape as the airtight sealing member (11 to
16), and connecting the airtight sealing member and the reinforcing plate
8 in the portions facing each other. With this method, the thermal
deformation which occurs between the airtight sealing member (11 to 16)
and the substrate Si is set off by the thermal deformation which occurs
between the reinforcing plate 8 and the Si substrate 1. As a result, the
problem of the conventional art, i.e., a crack of the Si substrate or
package leak due to fatigue of the airtight sealing portion, does not
easily occur.
In this case, however, the heat resistance between the Si substrate 1 and
the reinforcing plate 8 tends to be high, since the reinforcing member 8
is in contact with the Si substrate 1 only under the airtight sealing
portion. To prevent this, it is possible to make the reinforcing plate 8
be entirely in contact with the lower surface of the Si substrate 1, as
shown in FIG. 2, thereby lowering the heat resistance and to adjust the
material and the thickness of the reinforcing plate 8 and the
characteristics of the solder. As a result, the thermal deformation can be
set off in the same manner as in the aforementioned method.
As shown in the cross-section of the airtight sealing portion in FIG. 6
(perpendicular to the plane of FIG. 1), the rear end and side ends of the
reinforcing plate 8 may be directly bonded with the lower frame 11 of the
airtight sealing member. With this structure, deformation between the
airtight sealing member and the reinforcing plate 8 is directly
compensated, thereby increasing the degree of freedom in thermal
deformation minimizing design. In addition, since the Si substrate 1 does
not expose to the package exterior, protection thereof is ensured.
FIGS. 7A and 7B, 8A and 8B, and 9A and 9B are perspective views mainly
showing the Si substrate 1 to be mounted on the optical semiconductor
module shown in FIG. 2. A metallize pattern 4 for achieving soldered joint
with the airtight sealing member 11 is formed on the Si substrate 1. The
metallize pattern 4 is formed by pattern forming through deposition of
Au/Pt/Ti and lift-off thereof. The optical semiconductor element 6 and the
IC 7 are mounted on a pad metal having the same structure as that of the
metallize pattern 4 and a solder (an Au--Sn solder formed by multilayer
deposition of Au and Sn) formed on the Si substrate, and then subjected to
a heat treatment, thereby connecting the element 6 and the IC 7 with the
substrate. In this process, it is possible to employ a so-called flip chip
mounting method, in which the elements to be mounted on the substrate are
positioned by utilizing the surface tension of fused solder. The solder
groove 3 is to cause solder to flow on the rear side of the optical fiber
5, when the airtight sealing member is soldered with the substrate. The
solder groove 3 is formed by anisotropic etching of Si in the same manner
as in the process of forming the guide groove 2 for adjusting the position
of the optical fiber.
Examples of the method for forming the patterns of the guide groove 2 and
the solder groove 3, which cross each other, will be described with
reference of FIGS. 7A and 7B, 8A and 8B, and 9A and 9B. In the following,
the portions, which have already been described, are identified with the
same reference numerals as those used above, and detailed descriptions
thereof are omitted.
FIGS. 7A, 8A and 9A show shapes of masks, and FIGS. 7B, 8B and 9B show
shapes of etched portions (302, 305, 308). The narrower portion (300, 303,
307) of each mask is the guide groove 2 and the wider portion (301, 304,
306) is the solder groove 3.
FIGS. 7A and 7B show a case in which the grooves 2 and 3 are etched
simultaneously. As shown in FIGS. 7A and 7B, the portion where the two
grooves 2 and 3 cross is etched deeper. In FIG. 7B, the cross section
along the line L.sub.cs1 is indicated as V.sub.cs1, the cross section
along the line L.sub.cs2 is indicated as V.sub.cs2, and the cross section
along the line L.sub.cs3 is indicated as V.sub.cs3. In FIG. 8B, the cross
section along the line L.sub.cs4 is indicated as V.sub.cs4. As indicated
by the cross section V.sub.cs3, a multi-staged etching region is formed in
a peripheral portion of the line L.sub.cs3. The etching deformation is not
preferable, except for a case in which it is negligibly small relative to
the dimensions of the overall etched portion. The etching deformation can
be prevented by two-staged etching as shown in FIGS. 8A and 8B and 9A and
9B.
FIGS. 8A and 8B show a case in which the narrower groove 303 is etched
first, and subsequently, a second mask pattern is prepared to form the
wider groove. In this case, the second mask pattern 304 is arranged so as
not to cross with the first pattern 303, as shown in FIG. 8A. With this
arrangement of the patterns, a cross portion having a geometrical shape is
formed as shown in FIG. 8B, so that the etching deformation as shown in
FIGS. 7A and 7B can be avoided. However, if the bottom of a wider groove
is not completely etched so as to be surrounded by four (111) planes, the
portion, which is subjected to etching twice, is etched much deeper (see
the cross section V.sub.cs4. This shape of the etched portion is not
preferable, since, in this case, bubbles may be formed in the sealing
solder.
FIGS. 9A and 9B show a case in which the wider groove 306 is etched first,
and thereafter, the narrower groove is formed, in contrast to the case
shown in FIGS. 8A and 8B. In the case of FIGS. 9A and 9B, since the wider
groove is first formed independently, even if the bottom of the groove is
not completely etched so as to be surrounded by (111) planes, etching
deformation does not occur, unless the mask for forming the second groove
is not broken. However, it is necessary that the pattern of the narrower
groove should not cross with that of the wider groove, and that a much
narrower groove be formed in an end portion of the narrower groove so as
to reach a slant face of the wider groove, in order to connect the
narrower groove with the wider groove. As a result, a projection is formed
in the mask 307 of the narrower groove and an etch back region is formed
under the mask. However, the etch back region is stopped by a (111) plane
extended from the narrower groove on an extension line of a longer side of
the mask 307. At this time, it is necessary that the distal end of the
narrowest groove pattern be located on the (111) plane on the side of the
wider groove 306 and project from an end 309 of the bottom of the narrower
groove 307 toward the wider groove side, so as not to reach the bottom of
the wider groove, to prevent deformation of the bottom of the wider groove
308 as described above. In this manner, a substantially complete composite
groove as shown in FIG. 9B is formed. In this embodiment as described with
reference to FIGS. 2 and 6, the grooves are formed in the method shown in
FIGS. 9A and 9B.
FIGS. 10 and 11 are cross-sectional views of the Si substrate 1 formed in
the manner as described above, on a plane perpendicular to the plane of
FIG. 2.
FIG. 10 shows a cross section in a portion of the solder groove 3 shown in
FIG. 6, and FIG. 11 shows a cross section in a portion of the IC 7 for
transmitting or receiving data to or from the optical semiconductor
element. As described before, the side ends of the reinforcing plate 8 are
bonded with the lower frame 11 of the airtight sealing member. FIGS. 2 and
10 clearly show that the upper surface of the Si substrate 1 is sealed
airtight. Particularly as shown in FIG. 10, it is clear that the optical
fiber 5 is led outside through the sealed portion in the solder groove 3.
Thus, the optical semiconductor element 6 and the optical fiber 5 are
optically coupled with each other on the Si substrate 1 through the
mechanical positioning, thereby ensuring airtightness of the optical
semiconductor element 6 and the mechanical strength of the Si substrate 1.
Thus, the optical semiconductor element 6 is sealed airtight and the Si
substrate 1 is structurally reinforced without incurring an extra
producing cost for optical axis adjustment. It is therefore possible to
produce a reliable optical semiconductor module at a low cost.
In addition, since the Si substrate 1, which is a precision processed
element, can be mass-produced through semiconductor processes, it is
possible to mass-produce optical semiconductor modules without limit by
the throughput or cost of precision processed elements.
A process of producing the above optical semiconductor module will be
described. FIG. 12 is an exploded view of the first embodiment of the
present invention shown in FIG. 2. Details of the elements, such as the
semiconductor element, are not shown or described in the following.
In FIG. 12, the lower frame 11, made of Kovar alloy, has a partially
modified optical fiber inserting portion. The sealing insulators 12 and 14
are made of, for example, low melting point glass. The electrical signal
pin 13, the upper frame 15 and the airtight sealing cap 16, as well as the
lower frame 11, are made of the Kovar alloy.
Since the lower frame 11 has the modified portion, as shown in FIG. 12,
which corresponds to the solder groove 3 shown in FIG. 6, the optical
fibers can be soldered as shown in FIG. 10. If the lower frame 11 does not
have the modified portion, the sealing solder must be considerably thick
to achieve airtight sealing, in which case the solder material may flow
out or the width of the soldered portion may be different from place to
place. In addition, since the lower frame 11 is liable to be brought into
contact with the optical fiber 5, stress is easily applied to the optical
fiber 5 when the module is assembled. In an extreme case, the optical
fiber 5 may be damaged or cut off, in which case the reliability and the
yield of the modules will be lowered. The same problem arises in a case
where the optical fiber is replaced with an optical wave guide (to be
described later).
The process of assembling the module is as follows. First, the lower frame
11, the sealing insulators 12 and 14, the lead frame (the electrical
signal pin) 13 and the upper frame 15 are accumulated together and
subjected to a heat treatment, thereby forming the aforementioned airtight
sealing member as a unit. Then, the optical semiconductor element 6, the
IC 7 and the optical fiber 5 are successively or simultaneously mounted on
the Si substrate 1 by, for example, soldering. A preform solder 9, the Si
substrate 1, the airtight sealing solder 10 and the airtight sealing
member (the accumulated member consisting of the parts 11 to 15) are
successively accumulated, and the preform solder 9 and the sealing solder
10 are simultaneously caused to reflow. Thereafter, the semiconductor
element and the electrical pin 13 are wire-bonded and then, the sealing
cap 16 is sealed by means of seam welding. As a result, the optical
semiconductor module as shown in FIG. 2 is obtained.
(Second Embodiment)
The first embodiment shown in FIG. 2 is a so-called pigtail type optical
semiconductor module, in which optical fibers 5 project from the optical
semiconductor module. The pigtail type optical semiconductor module can be
changed to an optical connector type optical semiconductor module by
changing the structure of the substrate 1. The second embodiment is
different from the first embodiment only in the method of mounting the
optical fiber on the Si substrate. All the other portions of the second
embodiment are the same as in the first embodiment, and the description
thereof is omitted.
FIG. 13 shows a state in which elements are mounted on the Si substrate.
Optical fiber holders 19 and 20 made of Si comprising v grooves for
holding optical fibers can be produced by the same process for producing
the Si substrate 1. The optical fiber holders 19 and 20 are arranged in
advance such that an optical fiber exposing portion (the gap between the
optical fiber holders 19 and 20) for airtight sealing is formed and the
optical fibers are attached to the holders and the end faces are shaped by
polishing or the like. The optical fiber assembly thus formed is fit in an
enlarged solder groove 3' shown in FIG. 13 using the outermost two optical
fibers as positioning guides or in the flip chip mounting method for
mounting the optical fiber holder 19 itself on the Si substrate 1, thereby
optically coupling the fiber assembly with the optical semiconductor
element in the same manner as in the embodiment shown in FIG. 2.
Thereafter, the distal end of the optical fiber holder 19 may be polished,
so as to be aligned with the end face of the Si substrate 1. The groove on
the Si substrate side is flat, because the position of mounting the
optical fibers and the arrangement of the optical fiber array is defined
on the optical fiber holder side. Further, the purpose of the flat groove
is to absorb engagement deviation due to a processing error between the
optical fiber holder 19 and the Si substrate 1. Therefore, if the groove
on the Si substrate side is formed relatively greater, V grooves may be
formed also on this side. The above method, in which the optical fibers
and the optical fiber holders are assembled into one unit in advance as
shown in FIG. 13, is advantageous in that process risks can be dispersed
due to separation of assembling steps and the production yield can be
improved due to elimination of partial defects.
In the structure shown in FIG. 13, the lower surface of the optical fiber
holder 19 is adhered to the upper surface of the Si substrate 1. The
height of the optical fibers with respect to the reference surface, i.e.,
the surface of the Si substrate 1 on which the optical semiconductor
element is mounted, is determined with the groove processed accuracy of
the optical fiber holder. For this reason, a high process precision is
required for both the Si substrate 1 and the optical fiber holder 19. In
addition, the step of assembling the optical fiber holder and the
substrate requires a high accuracy.
To solve this problem, the following structure may be used. A guide groove
for defining the height and position of the optical fiber is formed on the
Si substrate side. The grooves on the optical fiber guide side are formed
to have a small width, so that the optical fiber holder 19 finally floats
above the Si substrate 1.
With this structure, the position and height of the optical fiber is
determined only on the Si substrate side, while the advantage of
assembling the optical fiber assembly in a separate step is being
maintained. If optical fibers are made in an array form, it is necessary
that the pitch of the grooves formed in the optical fiber holder 19 should
precisely coincide with that of the Si substrate 1. However, there will be
substantially no problem, if the grooves on the both sides are formed by
photolithography as in the semiconductor process.
In particular, even if the etching depth of the optical fiber holder 19 is
slightly changed, the pitch of the grooves will not change. Further, even
if the groove width is narrower, this will influence the assembly very
little. Therefore, the process accuracy specification is moderated and the
process yield can be improved very high.
As a result, since the overall yield is also improved, the above structure
is effective to one of the main objects of the present invention, i.e.,
reduction of the cost of the optical semiconductor module.
In the substrate produced in the manner as described above, a fixing plate
24 and a guide pin 34 are fixed at a weld fixing portion 25 and mounted on
the reinforcing plate 8. The fixing plate 24 is not limited to the shape
of this embodiment, but can be suitably selected in accordance with an
object to be mounted and the shape of the object.
Thereafter, a package is formed to be engaged with an optical connector, in
the same manner as in the second embodiment, thereby obtaining an optical
connector type semiconductor module. The structure of the optical
connector will be described later. The optical semiconductor module thus
produced provides the same effect as in the first embodiment.
(Third Embodiment)
A third embodiment differs from the first embodiment in that optical wave
guides are partially used in place of the optical fibers. The method for
mounting optical fibers on the Si substrate and the structure of the
optical connector are also different from the first embodiment. The third
embodiment will be described with reference to FIGS. 14 to 16.
FIG. 14 shows an example in which integrally formed optical waveguides 21
are optically coupled with external optical fibers (not shown). With this
structure, an optical fiber assembly need not be prepared in advance. In
addition, since the optical waveguides are formed integrally by the
semiconductor process, a further reliable optical semiconductor module can
be produced at much lower cost.
A structure of the optical connector will be described. FIG. 15 shows a
structure in which a guide pin groove 22 is formed on the Si substrate 1
shown in FIG. 14 and a guide pin 23 is inserted in the groove. The
structure is based on the assumption that there are a plurality of optical
transmission and reception channels. An optical connector for ribbon
optical fibers on the market, for connecting a plurality of optical
fibers, requires adjustment of the central axis of a connector and
inclination of arrangement axes of optical fibers.
In general, the adjustment of the axes is performed by using two guide
pins. FIG. 15 shows a state in which two guide pins are inserted in the
guide pin grooves. The guide pin grooves 22 are formed such that the
optical coupling axis thereof is adjusted to the optical axis of the
optical semiconductor element, like the optical fiber guide groove and the
optical waveguide 21. For this reason, the optical connector and the guide
pins are optically coupled only by mechanical assembly as in the
embodiment shown in FIG. 1. However, it is not desirable that the guide
pins be directly fixed to the Si substrate 1 in consideration of the
mechanical fragility of the Si substrate 1. Therefore, although the
position adjustment is performed by use of the Si substrate 1, the
mechanical fixture of the guide pins and suppression of deviation due to
an external force applied to the guide pins should be executed by another
measure.
FIG. 16 shows the third embodiment using the Si substrate 1 shown in FIG.
15. A fixture plate 24 for fixing the guide pins 23 has bent portions as
shown in FIG. 16, so that it can be deformed by external force. In other
words, the fixture plate 24, having a function of a spring, presses the
guide pins 23 against the guide pin grooves. The fixture plate 24 is
welded with the guide pins 23 at weld fixture portions 25. The fixture
plate 24 shown in FIG. 16 is mounted on the substrate, with the guide pins
inserted, in a preform solder reflow step in the assembling process
similar to that in the embodiments shown in FIGS. 2 to 14. A solder 10,
serving as adhesive, is contracted in a process in which a melted solder
is cooled and hardened. The solder 10 therefore works so as to move both
ends of the fixture plate 24 down with respect to the two guide pin
contact portions. As a result, the guide pins 23 are pressed into the
guide pin grooves of the Si substrate 10 by the elasticity of the fixture
plate 24. In this state, it is only necessary that the guide pins 23 be
fixed to the fixture plate.
In this embodiment, since the guide pins 23 are fixed to the fixture plate
24 and pressed into the guide pin grooves of the Si substrate 1 by the
elasticity of the fixture plate 24, the guide pins 23 are accurately
positioned by the Si substrate 1 and positional deviation of the guide
pins 23 due to external force is suppressed by the fixture plate 24. Thus,
both precise positioning of the guide pins and mechanical strength of the
connector can be simultaneously achieved. In this state, the effect of the
positioning mechanism by micromachining is maintained, while the fragile
Si substrate 1 is protected. For this reason, crack is not formed in the
Si substrate 1 in the positioning step or great stress due to external
force is not applied to the Si substrate 1. Therefore, a sufficient
reliability with respect to mechanical stress can be obtained.
As described above, the guide pins 23 must be fixed to the fixture plate 24
with a sufficient mechanical strength, preferably by welding, particularly
non-contact welding, such as laser welding or electron beam welding, in
order to avoid positional deviation or stress due to external force in the
welding process.
Further, in order to correct fine deviation between the guide pins and the
fixture plate, press the guide pins into the guide pin grooves of the Si
substrate 1 in the same direction, and keep the position of the inserted
guide pins constant, it is necessary that the guide pins 23 be fixed to
the fixture plate 24, preferably after the fixture plate 24 is fixed to a
supporting body, i.e., the reinforcing plate 8 in FIG. 16, and the fixture
plate 24 is pressed against the guide pins 23. In the third embodiment,
the same effect as in the first embodiment can be obtained.
(Fourth Embodiment)
In FIGS. 16 and 17, the fixture plate 24 is additionally provided. However,
to reduce cost by reducing the number of parts, the structure as shown in
FIG. 18 can be employed. In FIG. 18, an end of a reinforcing plate 8 is
worked into two stages to serve as a housing for holding a ferrule of an
optical connector. In this embodiment, the lower frame 11 is extended in
advance so as to function as a fixture plate and deformed into a
predetermined shape in guide pin inserting portions. Then, parts as shown
in FIG. 12, including the lower frame 11, is assembled into a unit, thus
reducing the number of parts and manufacturing steps. Further, since the
number of times of treating parts in assembling is reduced, errors in
handling the parts are reduced, resulting in improvement of the yield.
Thus, the overall cost is reduced and the productivity is improved. The
structure of the fourth embodiment is substantially the same as that of
the second embodiment except for the shape of the fixture plate. Needless
to say, this embodiment also provides the other effects of the second
embodiment.
(Fifth Embodiment)
FIG. 19 shows a fifth embodiment, which is different from the first
embodiment only in that guide pins 23 are enclosed by a reinforcing plate
8 and an airtight sealing cap 29 and are not exposed to the outside.
The structure shown in FIG. 19 is preferable to provide the optical
semiconductor module of the present invention with much higher
reliability. In this structure, since the guide pins 23 are positioned by
means of the Si substrate 1, it is preferable that the guide pins 23 be
located within the optical connector portion, whether a fixture plate is
employed or not. If the distal ends of the guide pins 23 project outside,
unexpected external force may be applied through the guide pins 23 to the
Si substrate 1. In this case, when the module is handled or mounted on a
circuit board or when the circuit board is maintained, a shock or
excessive force is applied to the guide pins, so that the Si substrate 1
may be easily broken. Thus, it is necessary that the distal ends of the
guide pins should not project outside, in a case where the positioning is
performed by means of the Si substrate. With the structure of the fifth
embodiment, the reliability is ensured even when the module is handled
after the production thereof is completed. Needless to say, this
embodiment also provides the other effects of the first embodiment.
As has been described above, the optical semiconductor element can be
optically coupled with an optical waveguide, such as an optical fiber, and
the optical semiconductor element can be airtight sealed only by a
mechanical assembling process. Moreover, since the reinforcing plate is
attached on the rear surface of the Si substrate, the Si substrate can be
prevented from crack due to the stress of the airtight sealing cap. The
present invention allows reduction in manufacturing cost of the
semiconductor module, substantial improvement of the productivity thereof,
and assured reliability. The present invention also allows a
large-capacity and high-quality signal transmission, which has been
characteristic to the optical communication technology, to be applied to
general industry equipment.
Additional advantages and modifications will readily occur to those skilled
in the art. Therefore, the invention in its broader aspects is not limited
to the specific details, representative devices, and illustrated examples
shown and described herein. Accordingly, various modifications may be made
without departing from the spirit or scope of the general inventive
concept as defined by the appended claims and their equivalents.
Top